there was a time we all used film, way back in the pre-digi-cam days. Though mostly with crappy old Agfa p&s film cams [yup, there was point and shoot/click before digital!] Cropping back then was done with a scissors

I'd say try it for yourself. Get a large 18 MP image, and downsize a copy to 4 megapixels. If you have them on the screen, you will not see a difference, and maybe the 4 megapixel one will actually look sharper! (since it's resize algorithm is more advanced than on-the-fly downsizing).

It may be more Aliased (jagged edges) which is perceived sharpness, and something you can do better in postproduction, actually.

_________________I take pictures so quickly, my highschool was "Continuous High".

All else being equal, an 18MP image resized to 4MP should look sharper than a camera native 4MP, as the 4MP is an interpolated output due to the bayer pattern. Reducing the 18MP to 4MP means each output pixel will contain the equivalent of more than 4 photosites of data and will gain positional accuracy. But you'd have to be really pixel peeping at this stage...

Look up Ken Rockwell's explanation of why mp dont matter. You can print a billboard with 4mp, you just have to stand back a bit to see a sharp image. I just bought myself a 1d classic, should be here tomorrow in the post. Its only 4mp but can do 8fps, has 45 af points and a pro body.